1. Field of the Invention
The present invention relates to an active control system for a LDC (Low-voltage DC/DC Converter) in an electric vehicle, and particularly to a LDC control for an electric vehicle which makes it possible to increase the miles traveled per charge in an electric vehicle and to increase the lifespan of a low voltage battery with the aid of a LDC voltage technique without the use of a battery sensor.
2. Description of Related Art
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term “hybrid vehicle” often refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors. However, other types of hybrids such as fuel cell electric hybrid vehicles are also encompassed by this category of vehicle. In the past decade, hybrid vehicles have become popular due to their increased fuel efficiency. Hybrid vehicles are able to increase fuel efficiency by providing a driving force to the drive train via an electric motor during (in the case of parallel hybrid vehicles) starting or accelerating and charging the battery during braking.
Typically, a high level controller (i.e., composed of a processor and a memory) is configured to control the entire operation of an electric vehicle. This high level controller is often referred to as an HCU (Hybrid Control Unit) or a VCU (Vehicle Control Unit). The HCU or the VCU is configured to communicate with a MCU (Motor Control Unit) which is a low level controller to thereby control the torque, speed and electric power torque output of the electric motor which is providing all or a portion of the driving force source. The HCU is further configured to communicate with an ECU (Engine Control Unit) which controls the engine. The engine in a hybrid vehicle generates a driving force which is applied to the drive train (i.e., the transmission) as well as a voltage which is applied to the battery to maintain the battery at a certain state of charge (SOC). To do so, the ECU performs relay control in relation with a driving force and an error diagnosis.
In addition, the HCU communicates with a BMS (Battery Management System) which is configured to detect the temperature, voltage, current and SOC (State Of Charge) of a battery and to manage the entire operational state of the battery, thus controlling the motor torque and speed depending on the state of the SOC and to further communicate with a TCU (Transmission Control Unit). The TCU determines and controls a speed change ratio depending on the speed of a vehicle and a driving demand from a driver, thus controlling and maintaining the speed of the vehicle required by the driver.
The communications between the HCU, a high level controller, and any of the low level controllers is often conducted via a CAN communication, so the information is exchanged between each of these controllers and a control signal is received and transmitted therebetween.
All vehicles which an electric motor are often equipped with an LDC (Low-voltage DC/DC converter) configured to reduce the high voltage coming from the high voltage battery into a low voltage direct current DC. The LDC is an electronic circuit which converts a source voltage from the high voltage battery of the vehicle which outputs a direct current (DC) from one voltage level to another for a plurality of different load requirements. In particular, the LDC is required to power accessories and the HVAC system.
Generally, the LDC is able to generate the maximum output irrespective of an alternator of an internal combustion engine and the vehicle RPM and operates with a 12V battery under all the conditions such as a driving, a stop, etc. During a high voltage battery charging procedure in an electric vehicle, since the low voltage battery is always being charged, the low voltage battery is often continuously over charged.
Furthermore, since the LDC output voltage is outputted at a set voltage of 14.3V, electric power is unnecessarily consumed due to the continuous LDC high voltage output (namely, 14.3V). Therefore, as a result the number of miles that the vehicle can travel per charge decreases. In addition, since the low voltage battery is continuously being charged, the lifespan of the battery decreases as a result of over charging and a gas generation phenomenon (gassing). This phenomenon occurs when excessive charging electrolyzes some of the water in the battery, emitting hydrogen and oxygen therein.